1. Field of the Invention:
This invention relates to a data processing device and, more particularly, to a device for processing a data sequence consisting of data correlated with each other.
2. Description of the Prior Art:
In transmitting normal audio and video signals for recording, it is known that the transmitted amount of information can be reduced to a great extent by an encoding arrangement wherein only the varying portions of these signals are transmitted by utilizing the correlation of audio signals on the time base and the spatial correlation of the video signal. The so-called high efficiency encoding methods utilizing such correlation of signals include a method of carrying out differential pulse code modulation (hereinafter referred to as DPCM). However, with the DPCM method applied to data, the level distribution of the data becomes extremely biased. FIGS. 1(a) and 1(b) of the accompanying drawings show the biased level distribution resultrng from application of the DPCM method to data. When pulse code modulated (hereinafter referred to as PCM) data, which has a level distribution as shown in FIG. 1(a), is subjected to a DPCM process, the level distribution becomes as shown in FIG. 1(b). As shown, the level generating probability becomes high around a point 0. Thus, with the data DPCM processed and non-linearly quantized, the number of quantizing bits of the data can be decreased. However, in the event of transmission of data having steep level variations, reduction in the number of quantizing bits is hardly possible and thus the length of the transmission bits cannot be shortened. FIGS. 2(a) and 2(b) show the data level distribution obtained in transmitting a data sequence which is replete with steep level variations. FIG. 2(a) shows the level distribution of PCM processed data and FIG. 2(b) that of DPCM processed data. As shown, there is some likelihood that the data would be deteriorated to a great degree with the transmission bit length shortened by merely carrying out a DPCM process. In other words there, are two requirements. One is the reduction in the transmission bit length, while the other is securing a sufficient dynamic range. Encoding methods for meeting these two requirements include variable length encoding methods. Considering the encoding method of Huffman code to be exemplary of the conventional variable length encoding methods, that method has presented the following problems: FIGS. 3(a), 3(b), 4(a) and 4(b) illustrate the problem of the conventional variable length encoding method. FIG. 3(a) shows an encoding format and FIG. 3(b) shows a manner in which an error is propagated.
Referring to FIG. 3(b), even if only one bit is erroneously encoded, the error is propagated by decoding the code into a number of erroneous data bits. Once a code error is made, therefore, the data transmitted thereafter becomes completely meaningless. In addition to that, the bit length for each data is varying. Therefore, it is difficult to compose a data frame for carrying out error correction at a high degree of efficiency. Further, in an encodrng method which is arranged, for such high efficiency error correction, to make the bit length of each data only an integer times as much as a prescribed number of bits, it becomes necessary to have some connecting bit within each group consisting of the prescribed number of bits. This results in an increase in the transmission bit length. FIGS. 4(a) and 4(b) show an encoding method of this kind. FIG. 4(a) shows a variable encoding format and FIG. 4(b) shows a transmission format which has the bit length of each data arranged to be in integer times as much as three bits.